According to the recent trend of lighting technology, an LED (Light Emitting Diode) has been employed as a light source.
A high-brightness LED is differentiated from other light sources in terms of various aspects such as energy consumption, lifetime, and light quality.
However, a lighting apparatus using LEDs as a light source may require additional circuits due to the characteristic of the LEDs which are driven by a constant current.
Examples of devices which have been developed to solve the above-described problem may include an AC direct type lighting apparatus.
In general, the AC direct type LED lighting apparatus is designed to drive LEDs using a rectified voltage obtained by rectifying commercial power. The rectified voltage may have a ripple of which the frequency is twice higher than that of the commercial power. Furthermore, each of the LEDs may be designed to have a light emission voltage Vf of 2.8V to 3.8V, for example.
Since the above-described AC direct type LED lighting apparatus directly uses the rectified voltage as an input voltage without using an inductor and capacitor, the AC direct type LED lighting apparatus has a favorable power factor.
The LEDs included in the LED lighting apparatus may be divided into a plurality of LED groups, and the plurality of LED groups may be sequentially turned on or off according to the rises or falls of the rectified voltage having a ripple.
The AC direct type LED lighting apparatus may include a plurality of switching elements (for example, FET) in order to control the turn-on/off of the LEDs. The plurality of switching elements may be configured for the respective LED groups, and the switching operations thereof can be controlled in response to the turn-on/off of the respective LED groups.
For example, when the LED lighting apparatus is designed to use an input voltage of AC 220V, a rectified voltage applied to the LED groups may have a peak voltage of about 311V.
The AC direct type LED lighting apparatus must be designed to be protected from a surge voltage. The surge voltage may be generated by various factors, and introduced into the LED lighting apparatus through an input voltage line.
When the LED groups are driven in the environment where a rectified voltage having a peak voltage of 311V is applied, a surge voltage of about 450V or more may have an influence on internal circuits. In general, the plurality of switching elements included in the LED lighting apparatus are designed to have a withstanding voltage of 450V to 700V. However, when a surge voltage equal to or higher than the designed withstanding voltage is applied, the switching elements may be damaged by the surge voltage. Thus, the conventional LED lighting apparatus may have a problem in terms of reliability.
The LED lighting apparatus may include switching elements capable of enduring a high voltage in order to secure stability from a surge voltage. However, since the switching elements capable of enduring a high voltage are expensive, the above-described method may serve as a factor which increases the manufacturing cost of the LED lighting apparatus.
The AC direct type LED lighting apparatus may be designed in such a manner that the LED group which first emits light among the plurality of LED groups includes a large number of LEDs, in order to prevent waveform distortion of the rectified voltage and to satisfy an operation characteristic (harmonic characteristic).
For example, the lamp of the LED lighting apparatus may include 96 to 104 LEDs, based on the environment in which an input voltage of AC 220V is applied.
The 96 to 104 LEDs may be divided into a plurality of LED groups, and each of the LED groups may include a different number of LEDs.
For example, when the LEDs are divided into four LED groups, the first LED group may include 30 LEDs, and each of the other LED groups may include 23 LEDs.
In this case, since the first LED group includes a larger number of LEDs than the other groups, the first LED group requires a high light emission voltage Vf. More specifically, the first LED group may be designed to require a light emission voltage Vf of 90V, and the other LED groups may be designed to require a light emission voltage Vf of 70V.
In this case, a difference between the light emission voltage Vf of the first LED group and the light emission voltage Vf of the other LED groups may be set to 20V or more. The difference between the light emission voltages Vf may serve as a factor which causes a difference in light intensity between the first LED group and the other LED groups. Furthermore, each of the other LED groups excluding the first LED group may have a low light intensity as the priority of the LED group is low, due to a difference in light emission time therebetween.
The LED lighting apparatus may be implemented with an L-tube having a similar structure to a fluorescent lamp. For this reason, an LED group has a low light intensity as the LED group is remote from the position at which the input voltage is applied. In reality, a difference between the light intensity of the first LED group to which the highest voltage is applied and the light intensity of the last LED group to which the lowest voltage is applied may be set to 70 or less.
Thus, the AC direct type LED lighting apparatus may have difficulties in providing a uniform light intensity (or luminance) at each position of the lamp.